Hydrogen peroxide -- the chemical that can turn a brunette into
an instant blonde -- appears on the icy surface of Jupiter's moon Europa,
according to a new discovery by NASA's Galileo spacecraft reported
in the March 26 edition of the journal Science.

"Hydrogen peroxide is a really weird chemical that reacts strongly
with almost everything," said Dr. Robert Carlson, principal investigator
for Galileo's near-infrared mapping spectrometer instrument, the device
that detected the chemical on Europa. Hydrogen peroxide is formed
constantly on Europa as Jupiter's energetic particles smash apart
molecules on the surface to produce new chemicals, Carlson said. This
process is called radiolysis.

Hydrogen peroxide does not appear naturally on Earth's surface,
partly because the surface is not hit by enough radiation to initiate
the process that creates the chemical. "On Earth, if we want hydrogen
peroxide, we have to make it in factories," Carlson said.

"Almost as soon as hydrogen peroxide is formed, it starts breaking
down," Carlson explained. "It's either destroyed by ultraviolet light
or changed by contact with other chemicals, so its life span on Europa
is only a few weeks to months." The hydrogen peroxide becomes another
reactive chemical called hydroxyl, and can ultimately produce oxygen
and hydrogen gas, said Carlson.

Because Europa's surface chemicals are constantly being made
and destroyed, it's hard to study its long-term chemical history,
Carlson said. "On the other hand, we are interested in watching
changes in chemical composition over short periods of time. By
studying chemical processes on Europa and the other moons of
Jupiter, we can learn more about how those moons interact with
Jupiter, and how similar processes occur elsewhere in our solar
system."

Galileo's near-infrared mapping spectrometer works like a
prism, breaking up infrared light that is not visible to the
naked eye. Since different chemical molecules absorb infrared
light differently, scientists can study the light patterns and
determine what chemicals are present. In this case, the
instrument was used to study infrared light from Europa's
surface, and it detected dark areas of hydrogen peroxide. The
human eye would not normally see the hydrogen peroxide on Europa,
because it is dissolved in surface ice and has no color.

Galileo's instruments had previously detected several other
chemicals on Europa's surface, including sulfur dioxide, water
ice, carbon dioxide, and possibly salt molecules containing
water. Carlson and other scientists will have another chance to
study the chemistry of Europa's surface when the Galileo
spacecraft flies by Europa on November 25.

Galileo has been studying Jupiter, its moons and its magnetic
environment for more than three years. Its primary mission ended
in December 1997, but the spacecraft is in the midst of a two-year
extension called Galileo Europa Mission.

The Galileo mission is managed by JPL for NASA's Office of
Space Science, Washington, DC. JPL is a division of the
California Institute of Technology.